1. Field of the Invention
The invention relates to a method for producing sheet-metal container bodies having a longitudinal seam welded by a laser beam, and to an apparatus for performing the method.
2. Description of the Related Art
Published Federal Republic of Germany Patent Application (Offenlegungsschrift) No. 27 01 427 discloses a method for producing container bodies from sheet metal with straight longitudinal ends joined into a longitudinal seam by abutting the edges of the longitudinal end, followed by laser beam welding of the abutted edges. With this method, satisfactory seams are attainable at welding speeds of up to approximately 30 m/min. At higher welding speeds, irregularities or flaws, such as cracks, shrink holes or pores, have been found to appear in the welded seam. Such irregularities occur in part because of stresses due to a steep temperature drop in the areas of the metal sheet adjoining the abutted edges.
Published Federal Republic of Germany Patent Application (Offenlegungsschrift) No. 29 20 428 discloses a method and apparatus for producing laser beam welded hollow sections (pre-forms) in which both longitudinal ends of the pre-formed section are bent in the same direction and are oriented radially outwardly and pushed together before being welded. In this method, it is accordingly difficult, without further machining, to obtain a smooth welded seam.
Published Federal Republic of Germany Patent Application (Offenlegungsschrift) No. 32 19 252 discloses a method for welding metal parts that have a particularly defined geometric shape which they must retain and a relatively great sheet thickness, for example, a platform and web of a brake shoe. The metal parts in their final shape are urged into contact with one another and are welded together by means of a focused laser beam, electron beam or plasma beam. In order to counteract the strain in the metal parts caused by the heat of welding, an additional force is exerted on the connection of the metal parts in the vicinity of the welding site, for instance by means of a roller.
Published Federal Republic of Germany Patent Application (Offenlegungsschrift) No. 26 47 082 discloses a method in which two strips that each move in their longitudinal extension are joined at an angle to form a mutually overlapping connection in the direction of movement and are pressed together by a pair of pressure rollers. A focused laser beam is aimed at the region in which the two strips run together, effecting a continuous weld of the overlapping seam.
Finally, U.S. Pat. No. 4,237,363 discloses a method for spot welding or line welding together two flat stacked sheets in which an electron beam or laser beam is aimed at the outside of one of the sheet elements. An attendant disadvantage of this method is that the surface of one of the sheet elements is marred by the electron or laser beam.